The present invention relates to a technique of sealing light-emitting elements with a thin film.
As an example of known light-emitting elements, there is an organic EL (electroluminescent) element that emits light by using a light-emitting element having a thin organic light-emitting film composed of a multi-layered organic compound that is interposed between two electrodes and emits light by excitation due to an electric field. In a process of manufacturing a device having organic EL elements, in order to prevent an organic light-emitting material and a cathode, which includes an electron injection layer formed of, for example, calcium, magnesium, or aluminum complex, from deteriorating due to the presence of or contact with air or moisture, a sealing process is performed. As examples of known sealing techniques, thin film sealing techniques of covering organic EL elements with an extremely thin inorganic compound film are known (see, for example, JP-A-9-185994, JP-A-2001-284041, JP-A-2000-223264, and JP-A-2003-177244). In these techniques, the inorganic compound film serves as a gas barrier layer that blocks air.
In general, it is necessary to form a gas barrier layer with a large thickness in order that the gas barrier layer provides a sufficient reliability (in particular, coating reliability with respect to fine contamination that cannot be blocked even in a clean room). On the other hand, in the thin film sealing techniques, organic EL elements are formed on a substrate and a thin gas barrier layer is formed on the substrate so as to cover the organic EL elements by means of a vapor growth method, for example. At this time, a step difference, such as unevenness, may occur on a surface of the gas barrier layer, due to the presence of insulating pixel partition walls for separation among a plurality of elements. When the gas barrier layer having the step difference is formed to be uniformly thick, the stress is noticeably concentrated in a portion having the step difference, which causes the gas barrier layer to easily crack or be peeled off. Further, in the case where a gas barrier layer is a transparent and high moisture-resistance inorganic compound layer, which is formed of, for example, a silicon compound, the inorganic compound layer has a density and elastic modulus (Young's modulus) higher than those of an organic compound layer. Accordingly, a crack easily occurs due to the stress concentration.
If the gas barrier layer cracks or is peeled off, moisture contained in atmospheric air permeates into the organic EL elements. Accordingly, a problem occurs in that the organic EL elements are significantly deteriorated. Further, when the gas barrier layer is formed of an organic compound material having a low elastic modulus in order to prevent formation of cracks or is formed to be extremely thin, it is difficult to obtain sufficient sealing reliability even if the gas barrier layer does not crack or is not peeled off, which also causes early deterioration of the organic EL elements.